ENIAC, short for Electronic Numerical Integrator And Computer, was the first general-purpose electronic computer. It was the first Turing-complete, digital computer capable of being reprogrammed to solve a full range of computing problems,^[3] although earlier machines had been built with some of these properties. ENIAC was designed and built to calculate artillery firing tables for the U.S. Army's Ballistic Research Laboratory.

The ENIAC held immediate importance. When it was announced in 1946 it was heralded in the press as a "Giant Brain." It boasted speeds one thousand times faster than electro-mechanical machines, a leap in computing power that since then has typically taken fifteen years rather than just three. This mathematical power, coupled with general-purpose programmability, excited scientists and industrialists. The inventors promoted the spread of these new ideas by teaching a series of lectures on computer architecture.

The ENIAC's design and construction were financed by the United States Army during World War II. The construction contract was signed on June 5, 1943, and work on computer was begun in secret by the University of Pennsylvania's Moore School of Electrical Engineering starting the following month under the code name "Project PX". The completed machine was unveiled on February 14, 1946 at the University of Pennsylvania, having cost almost $500,000. ENIAC was shut down on November 9, 1946 for a refurbishment and a memory upgrade, and was transferred to Aberdeen Proving Ground, Maryland in 1947. There, on July 29, 1947, it was turned on and would be in continuous operation until 11:45 p.m. on October 2, 1955.

ENIAC was conceived and designed by John Mauchly and J. Presper Eckert of the University of Pennsylvania. The team of design engineers assisting the development included Bob Shaw (function tables), Chuan Chu (divider/square-rooter), Kite Sharpless (master programmer), Arthur Burks (multiplier), Harry Huskey (reader/printer), Jack Davis (accumulators) and Iredell Eachus Jr.